Go Chi HTTP/3 0-RTT Anti-Replay Verification and Method Whitelisting

QUIC and HTTP/3 0-RTT (Early Data) handshakes introduce severe replay attack vulnerabilities where on-path network adversaries can duplicate non-idempotent TLS records. This guardrail mandates strict HTTP method whitelisting and cryptographic anti-replay verification within Go Chi middleware, rejecting unverified mutating requests with HTTP 425 Too Early. Production services must guarantee that early data is restricted exclusively to safe, idempotent operations and verified against replay caches before execution.

--- description: Go Chi HTTP/3 0-RTT Anti-Replay Verification and Method Whitelisting - QUIC and HTTP/3 0-RTT (Early Data) handshakes introduce severe replay attack vulnerabilities where on-path network adversaries can duplicate non-idempotent TLS records. This guardrail mandates strict HTTP method whitelisting and cryptographic anti-replay verification within Go Chi middleware, rejecting unverified mutating requests with HTTP 425 Too Early. Production services must guarantee that early data is restricted exclusively to safe, idempotent operations and verified against replay caches before execution. globs: **/*.go, cmd/**/*.go, internal/api/**/*.go, internal/transport/http/**/*.go alwaysApply: true verified_by: "agentrules.org" license: "CC-BY-4.0" source: "https://agentrules.org/rules/go-chi-http3-0rtt-anti-replay-guardrail-go-chi-http-3-0--378" --- # Go Chi HTTP/3 0-RTT Anti-Replay Verification and Method Whitelisting > **Severity**: CRITICAL | **Category**: backend > **Anti-Pattern Warning**: Unconditional Execution of State-Mutating Handlers on QUIC 0-RTT Early-Data Payloads ## System Constraints You are a Principal Software Architect enforcing QUIC and HTTP/3 zero round-trip time (0-RTT) security standards in Go Chi applications. Mandate cryptographic anti-replay verification and strict RFC 8470 method whitelisting in middleware. Never allow state-mutating requests (POST, PUT, PATCH, DELETE) or replayed idempotent requests to execute over unconfirmed 0-RTT early data. ## Strict Guidelines - Engineers MUST ALWAYS inspect HTTP/3 early data state in Chi middleware using connection context or the standard 'Early-Data' (RFC 8470) header before executing business logic. - Engineers MUST immediately abort processing and respond with HTTP status 425 (StatusTooEarly) when any non-safe method (POST, PUT, PATCH, DELETE) is received during a 0-RTT handshake. - Services MUST implement a distributed or bounded in-memory replay cache (e.g., sliding window bloom filter or token store) to track unique 0-RTT request identifiers for whitelisted safe methods. - Components NEVER execute database mutations, payment transactions, or side-effecting operations inside an early-data execution path. - Code SHOULD configure HTTP/3 listeners with quic.Config.Allow0RTT set cautiously, pairing it with anti-replay middleware mounted at the root router level prior to authentication handlers. ## Bad vs Good Implementations ### Vulnerable Chi HTTP/3 Route Handling 0-RTT Without Anti-Replay Protection #### Bad Antipattern (AI Common Hallucination) > **Why it fails**: The HTTP/3 server accepts early data without checking if incoming requests are 0-RTT. A network attacker capturing the client's initial 0-RTT flight can replay the POST request, causing duplicate ledger transfers or duplicate database side-effects. ```go package main import ( "net/http" "github.com/go-chi/chi/v5" "github.com/quic-go/quic-go/http3" ) func SetupRouter() http.Handler { r := chi.NewRouter() // VULNERABLE: Direct registration of state-mutating handlers without early-data inspection. // An attacker capturing 0-RTT initial QUIC packets can replay fund transfers or resource // creation requests multiple times without detection. r.Post("/api/v1/transfers", func(w http.ResponseWriter, r *http.Request) { // State mutation executed directly on potentially replayed 0-RTT packet w.WriteHeader(http.StatusCreated) w.Write([]byte(`{"status":"transferred"}`)) }) return r } func RunServer(handler http.Handler) error { server := &http3.Server{ Addr: ":443", Handler: handler, } return server.ListenAndServeTLS("cert.pem", "key.pem") } ``` #### Production Standard (Correct) > **Standard**: The middleware intercepts early data using RFC 8470 semantics. Any non-safe HTTP method (like POST) arriving over 0-RTT early data is immediately rejected with HTTP 425 StatusTooEarly before reaching application logic. Safe methods calculate a cryptographic fingerprint and verify against a replay cache to thwart duplicate processing. ```go package main import ( "crypto/sha256" "encoding/hex" "net/http" "sync" "time" "github.com/go-chi/chi/v5" "github.com/quic-go/quic-go/http3" ) type ReplayCache struct { sync.Mutex seen map[string]time.Time ttl time.Duration } func (rc *ReplayCache) IsReplayed(key string) bool { rc.Lock() defer rc.Unlock() now := time.Now() if expiry, exists := rc.seen[key]; exists && now.Before(expiry) { return true } rc.seen[key] = now.Add(rc.ttl) return false } // AntiReplay0RTT enforces RFC 8470 anti-replay invariants func AntiReplay0RTT(cache *ReplayCache) func(http.Handler) http.Handler { return func(next http.Handler) http.Handler { return http.HandlerFunc(func(w http.ResponseWriter, r *http.Request) { // Check if connection or request flag marks 0-RTT Early Data isEarlyData := r.Header.Get("Early-Data") == "1" if isEarlyData { // INVARIANT 1: Disallow non-idempotent / state-mutating methods switch r.Method { case http.MethodGet, http.MethodHead, http.MethodOptions: // Safe methods permitted subject to cache verification default: w.Header().Set("Retry-After", "1") http.Error(w, "Too Early: mutating methods prohibited in 0-RTT", http.StatusTooEarly) return } // INVARIANT 2: Verify request fingerprint against replay cache hash := sha256.Sum256([]byte(r.Method + ":" + r.URL.RequestURI() + ":" + r.Header.Get("Authorization"))) fingerprint := hex.EncodeToString(hash[:]) if cache.IsReplayed(fingerprint) { http.Error(w, "Too Early: duplicate 0-RTT request detected", http.StatusTooEarly) return } } next.ServeHTTP(w, r) }) } } func SetupRouter(cache *ReplayCache) http.Handler { r := chi.NewRouter() r.Use(AntiReplay0RTT(cache)) r.Post("/api/v1/transfers", func(w http.ResponseWriter, r *http.Request) { w.WriteHeader(http.StatusCreated) w.Write([]byte(`{"status":"transferred"}`)) }) return r } ```

Architectural Specification & Invariant Rationale

Architectural Invariant Design: Go Chi HTTP/3 0-RTT Anti-Replay Verification and Method Whitelisting

Go Chi HTTP/3 0-RTT Anti-Replay Verification and Method Whitelisting defines an industrial-grade behavioral standard for backend engineering. QUIC and HTTP/3 0-RTT (Early Data) handshakes introduce severe replay attack vulnerabilities where on-path network adversaries can duplicate non-idempotent TLS records. This guardrail mandates strict HTTP method whitelisting and cryptographic anti-replay verification within Go Chi middleware, rejecting unverified mutating requests with HTTP 425 Too Early. Production services must guarantee that early data is restricted exclusively to safe, idempotent operations and verified against replay caches before execution. Modern software architectures require strict adherence to deterministic patterns to guarantee high availability, maintainability, and zero security vulnerabilities.

Framework Paradigm Shift & Drift MechanicsLLMs are trained on millions of open-source repositories containing outdated code, legacy idioms, and unpatched antipatterns. When coding assistants generate implementations for this stack, they default to common statistical tokens: Unconditional Execution of State-Mutating Handlers on QUIC 0-RTT Early-Data Payloads Without an explicit system instruction file, developers spend hours debugging silent failures.

Failure Modes & Production Blast Radius

Hazard Analysis: What Breaks Without This Rule

The following failure modes have been cataloged from hundreds of hours of production code reviews where AI assistants produced non-compliant implementations:

Failure Mode	AI Symptom (The Anti-Pattern)	Severity	Production Impact & Remedy
AI Hallucination & Deprecation Drift	Unconditional Execution of State-Mutating Handlers on QUIC 0-RTT Early-Data Payloads	Critical	Violating this industrial standard introduces regression bugs, security risks, and unexpected runtime failures in production. Enforce explicit behavioral system directives across all AI coding assistants in your repository.
Silent Architecture Inconsistency	AI assistants produce mixed paradigms across files, creating fragmented codebase conventions.	Medium	Increases cognitive load during code reviews and leads to maintenance debt across engineering teams. Pin project conventions in .cursor/rules, CLAUDE.md, and AGENTS.md so all team agents follow identical guardrails.

Architectural Directives in Detail

Step-by-Step Production Directives

Each rule constraint below is injected into the AI agent's system prompt to establish deterministic boundaries:

Engineers MUST ALWAYS inspect HTTP/3 early data state in Chi middleware using connection context or the standard 'Early-Data' (RFC 8470) header before executing business logic.

Rationale:AI models frequently generate unconstrained code here because statistical language distributions lack project-specific architectural context. Mandating this directive ensures that generated code adheres to verified industrial production requirements.